No. 55: Jan-Feb 1988
In a recent issue of the New Scientist, B. Fox mused about the weird world of electromagnetic transmissions and unidentified audio-frequency humming. We and our complex array of high-tech gadgetry are continuously bombarded by all manner of electrical and electromagnetic signals, noise, and transients. A particularly annoying source of unwanted signals impinging upon European radios is the Soviet Woodpecker over-the-horizon radar. In some bands, radio hams are blasted off the air when the Woodpecker is aimed at them.
So much for electromagnetic problems. In the audio range of the sound spectrum, Fox brings up the topic of those still unidentified hums that afflict a small group of people, who are now known as "hummers." Fox himself turns out to be a hummer.
"By coincidence, I happen to be blessed, or cursed, with good low-frequency hearing. For several years now, I have intermittently heard a curious low-frequency sound coming from a deep below the high ground around my home in Hampstead Heath in London. Most of the time it is swamped by other noises, because human hearing adjusts sensitivity to compensate for background noise. The noise is an intermittent rumble, like a very distant generator, or the compressor for a pneumatic drill, coming on and off load. Most people cannot hear it at all. I usually hear it only in the still of night."
Fox applied considerable effort in trying to find the source of the sound to no avail. The hum has been recorded and analyzed. It peaks at about 48 Hertz, and thus seems unrelated to the British 50-Hertz power mains.
(Fox, Barry; "Things That Go Buzz in the Night," New Scientist, p. 72, October 8, 1987.)
Reference. Other natural hums are described in GSH5 in our catalog: Earthquakes, Tides. Details on this book are available here.